The present application extends a successful multifaceted investigation of host resistance to viral infection. The strengths of our approach include: 1) an unbiased component based on mutagenesis combined with a hypothesis-driven component; 2) the study of distantly related organisms (mice and Drosophila) to appreciate which elements of defense are conserved; 3) the embrace of new and powerful methods to support our efforts. In our work to date, we have collectively identified new sensors (e.g., LGP2; DICER-2) necessary for activation of antiviral defenses, and delineated pathways of response to viruses, both at a biochemical level and in terms of communication between cells. We have identified previously unknown molecular participants in host defense. Among these are channel proteins (SLC15A4; KCNJ8/SUR2), transcription factors (IKB;AKIRIN2), proteins concerned with membrane trafficking or organellar mobility (AP3B1; STING; TR1M56; ATG9A; UNC93B), cell stress (SLFN2), post-translational modification (TRIM56; TR1M23), and endosome physiology (SLC15A4). Some of these proteins are members of extended families and may open the way to broad new models of host defense. Others highlight the importance of intermediary steps in host defense (e.g., the movement of molecules within cells) in a way that has not been considered before. Each participating group (Dallas, Osaka, and Strasbourg) has its special talents, and these have been combined to take us beyond genetics per se, incorporating new technologies that will accelerate the discovery of essential elements of the host defense apparatus. We recognize that it is not enough to possess a list of parts to understand how a machine operates. As new proteins are shown to be essential for particular aspects of host defense, we will establish how they interact with one another and/or other proteins to support resistance; how they catalyze particular reactions within cells, and how they drive or suppress the expression of genes in what we see as a highly dynamic process. We view the continuation of this POl as an opportunity to build upon an approach with established productivity: one that has generated new molecules, concepts, and reagents for use by the scientific community as a whole. The POl has been, and will continue to be, highly collaborative in the exchange of methods, genetic materials, and most importantly, ideas, ultimately derived from genetics.